Submitted to: Photosynthetica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/24/2005
Publication Date: 6/1/2005
Citation: Bunce, J.A. 2005. Seed yield of soybeans with daytime or continuous elevation of carbon dioxide under field conditions. Photosynthetica. 43:435-438. Interpretive Summary: In investigating responses of crops to projected increases in the concentration of carbon dioxide in the atmosphere, some studies have added carbon dioxide only in the daytime, while others have added carbon dioxide continuously. I tested whether there was a difference between these two methods, by comparing the yields of soybeans grown each way. There was a difference in yield depending on which method was used to provide the high carbon dioxide concentration. Adding carbon dioxide continuously always resulted in higher yields. This shows that in studies of crop responses to elevated carbon dioxide, how the carbon dioxide is added makes a difference. This information will be of use to scientists studying the impact of rising atmospheric carbon dioxide on crops and other plants.
Technical Abstract: Some studies of responses of plants to elevated concentrations of carbon dioxide added carbon dioxide only in the daytime, while others supplied carbon dioxide continuously. I tested whether these two methods of providing elevated carbon dioxide treatments produced differences in the seed yield of soybeans. Tests were conducted for four growing seasons, using open top chambers, with soybeans rooted in the ground in field plots. One third of the chambers were flushed with air at the current ambient concentration of carbon dioxide, one third had carbon dioxide 350 ppm above ambient during the daytime, while one third had carbon dioxide 350 ppm above ambient for 24 h per day. Continuous elevation of carbon dioxide increased seed yield by an average of 62% over the four years compared with the ambient carbon dioxide treatment, while daytime elevation of carbon dioxide increased seed yield by 34%. Higher seed yield for continuous elevation of carbon dioxide compared with daytime elevation occurred each year. In comparing years, the relative yield disadvantage of daytime only elevation of carbon dioxide decreased with increasing overall seed yield. On days with high water vapor pressure deficits, soybean canopies with daytime elevation of carbon dioxide had smaller midday extinction coefficients for photosynthetically active radiation than canopies with continuously elevated carbon dioxide, because of a more vertical leaf orientation. The results indicated that seed yield of soybean at elevated carbon dioxide varied depending on whether elevated carbon dioxide was also provided at night, with much greater yield stimulation for continuous than for daytime only elevation of carbon dioxide in some years.